Faraday rotation in femtosecond laser micromachined waveguides

Phase customization in photonic integrated circuits with trimmed waveguides

Accurate photon phase control on a chip is essential to improve the expandability and stability of photonic integrated circuits (PICs). Here, we propose a novel, to the best of our knowledge, on-chip static phase control method in which a modified line is added close to the normal waveguide with a lower-energy laser. By controlling the laser energy and the position and length of the modified line, the optical phase can be precisely controlled with low loss and a three-dimensional (3D) path. Customizable phase modulation ranging from 0 to 2π is performed with a precision of λ/70 in a Mach-Zehnder interferometer. The proposed method can customize high-precision control phases without changing the waveguide's original spatial path, which is expected to control the phase and solve the phase error correction problem during processing of large-scale 3D-path PICs.

Magneto-optical imaging feature extraction of micro-gap weld joint under nonuniform magnetic field excitation

To reduce the effect of the nonuniformity of magnetic field excitation on micro-gap weld joint magneto-optical (MO) imaging, a new experimental system based on the Faraday MO effect to detect micro-gap welds (gap width less than 0.1 mm) under nonuniform magnetic field excitation was developed. Horseshoe permanent magnets were used to magnetize the weldment and establish a nonuniform magnetic field at the welding joint. MO images of the micro-gap weld joint were captured using an MO sensor under nonuniform magnetic field excitation. After analyzing the distribution characteristics of the magnetic induction intensity in the weld joint area, a characterization method for the weld zone slope was proposed. The weld zone slope could accurately determine the MO imaging effects under the nonuniform magnetic field. A model based on an error backpropagation (BP) neural network was used to predict the offset of the weld joint center at each moment, and the results performed by BP were utilized to optimize the measured value of the weld joint center. Experimental results show that it can accurately extract the position of micro-gap welds under nonuniform magnetic field excitation.

Fabrication of magneto-optical waveguides inside transparent silica xerogels containing ferrimagnetic Fe3O4 nanoparticles

Magneto-optical waveguides with a refractive-index change were successfully fabricated inside silica xerogels containing ferrimagnetic Fe₃O₄ nanoparticles (NPs) using femtosecond laser processing. Aminopropyltriethoxysilane-derived xerogels were prepared via a sol-gel process with aqueous solutions of Fe₃O₄ NPs synthesized by coprecipitation. The mass/volume concentration of Fe₃O₄ NPs in the xerogels was determined by comparing the absorbance of the xerogel with that of an aqueous solution of Fe₃O₄ NPs. We evaluated Faraday rotation angles for light propagating through waveguide structures in xerogels containing Fe₃O₄ NPs at mass/volume concentrations of 0.087 and 0.148 mg/cm³ at a wavelength of 488 nm. Ferrimagnetic saturation of the Faraday rotation angle was observed, which is consistent with the magnetization curves measured at room temperature. Magneto-optical waveguides can potentially be used to produce micro-sized Faraday devices, such as optical isolators, high-density magnetic recording devices, and optical sensors, which can be integrated with optical and electronic hybrid circuits.

Competition of Faraday rotation and birefringence in femtosecond laser direct written waveguides in magneto-optical glass

We consider the process of Faraday rotation in femtosecond laser direct-write waveguides. The birefringence commonly associated with such waveguides may be expected to impact the observable Faraday rotation. Here, we theoretically calculate and experimentally verify the competition between Faraday rotation and birefringence in two waveguides created by laser writing in a commercial magneto-optic glass. The magnetic field applied to induce Faraday rotation is nonuniform, and as a result, we find that the two effects can be clearly separated and used to accurately determine even weak birefringence. The birefringence in the waveguides was determined to be on the scale of Δn = 10(-6) to 10(-5). The reduction in Faraday rotation caused by birefringence of order Δn = 10(-6) was moderate and we obtained approximately 9° rotation in an 11 mm waveguide. In contrast, for birefringence of order 10(-5), a significant reduction in the polarization azimuth change was found and only 6° rotation was observed.

Study of nanosecond pulsed magnetic fields using temporally resolved Faraday rotation through a magneto-optical waveguide

We have measured magnetic fields up to 17.7 T with a rise time of 75 ns using temporally resolved Faraday rotation of a single longitudinal mode laser beam through a magneto-optically active bulk waveguide. We believe this to be the first time that such large, rapidly varying magnetic fields have been measured with this class of materials (multicomponent terbium borate glass). As there was no measurable lag between the magnetic field inferred from the angle of rotation of the laser beam and the electromagnetically measured field, our sample of terbium borate glass has a spin-lattice relaxation time of a few tens of nanoseconds at most at approximately room temperature (300 K). The highest peak magnetic fields were measured in wire-array Z-pinch experiments on a 0.5 MA pulsed power machine.